[Openmcl-devel] Strange LISP Clozure problems

Lonnie Cumberland lonnie at biofuelstechnologyinc.com
Fri Oct 1 06:57:17 PDT 2010

Greetings All,

I am working on some code in lisp and basically have 2 lists now after
originally trying with just one where I had the same problem. (I also
had a plist version but still get the same problem.)

I make a list for a format of

((1  nil nil 1)
(n nil nil 1))

call it *db*. I then add some values such that the first "nil" is made
into a list. [ie.. (1 (2) nil 1) ] and then do this for the whole list
in *db* with the function below.

(defun add-mod-pres (b)
         #'(lambda (row) (setf  (second row) (nconc (second row) (list
(mod (first row) b))))) *db*)

The problem comes when I try to make a copy of the *db* and then
change some value in the "copied" db.

(setf tempdb (copy-list (remove-if-not #'(lambda (row) (equal (first
(last row)) (list j))) *db*)))

The result I am getting is that things as also being changed in the
original *db* as well and it look as though there is something going
on with LISP using pointers instead of actually making a copy.

The basic code problem is to have my list like:

((1  nil nil 1)
(n nil nil 1))

and while iterating over some other lists that I have, I grow each
list like the below example of a single sublist within *db*:

Iteration 1
(1 (2) (1) 1)

Iteration 2
(1 (2 1) (1 5) 1)


Iteration 10
(1 (2 1 3 4 5 4 3 2 1 0) (1 5 3 2 4 5 4 4 5 3) 1)


What I am currently getting is that when I modify the (1 5 .... ) list
then it also seems to modify the (2 1 .....) list in the *db* and this
also happens if I modify the (1 5 ....) list in the tempdb which also
modifies the *db* list.

There seems to be some shared memory in the lists going on and I don't
know how to stop it.

Could the "lambda" or "mapcar" functions be the problem?

Kind Regards and have a great day,
Lonnie T. Cumberland

"BTE, bringing people together today to meet the world's energy needs
of tomorrow......"


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